1. Field of the Invention
The present invention relates to a gas-fired heating apparatus with at least one gas burner, which is arranged within a combustion chamber; an associated combustion gas/air supply system, which has an inlet for combustion gas and combustion air, which is arranged outside of the combustion chamber on the heating apparatus; and an oscillation-damping air supply chamber with at least one air inlet.
2. Related Art
These types of gas-fired heating apparatus typically include gas-fired water heaters or gas-fired heating units, like those used for industrial heating and fireplaces in homes.
Gas-fired water heaters are used in many different forms and in many different power stages in different applications both in the private and also the industrial sector. This sort of gas-fired water heater is used, for example, for preparation of heated service water in industry or of hot water for heating in homes.
A special embodiment of this sort of gas-fired hot water preparing apparatus is the so-called “water heater” marketed in the U.S.A., which typically prepares shower water in workplaces or the like. For example one such “water heater” is described in U.S. Pat. No. 4,953,510, which comprises a thermally insulated storage tank for supplying heated water. This water heater is combined with a heating device for heating the water. The device most frequently used for heating the stored water comprises an open atmospheric gas burner that produces hot exhaust gases including combustion products, which act on the bottom of the water storage tank and subsequently rise through a long exhaust pipe, which extends through the center of the storage tank. In this type of water heater the hot gases flowing upward in the exhaust pipe contact the inner surfaces of the pipe, while the water in the storage tank contacts with the outer surface of the pipe. While the combustion proceeds, the water within the storage tank is heated by conduction through the wall of the exhaust pipe.
Increasingly strict regulations to prevent pollution, especially when flammable vapors reach the open combustion area, and in regard to improvements of exhaust gas quality, have led to developments in the water heater field, which have produced a nearly completely closed combustion chamber (burning chamber), in which a complete pre-mixing gas burner, a so-called pre-mix burner is arranged. This sort of water heater is, e.g., described in U.S. Pat. No. 5,875,739 or U.S. Published Patent Application US 2003/0111 023 A1.
In German Patent Application 10 2004 006 091.6-13, which discloses the same subject matter as co-pending U.S. patent application Ser. No. 10/978,571, pressure conditions can occur in the combustion chamber of the above-described gas-fired heating apparatus with an atmospheric, complete pre-mixing gas burner arranged in an almost completely closed combustion chamber, such that resonances are produced so that the system oscillates. These resonance oscillations have the following disadvantages:                no stable or uniform combustion is possible and exhaust gas quality is poor;        disturbing loud noise is observed; and        a backfire of flames through the combustion medium is possible, depending on the turbulence in the combustion chamber.        
In order to prevent resonances from occurring in a gas-fired heating apparatus with at least one atmospheric gas burner, which is arranged within a nearly completely or completely closed combustion chamber and which is associated with a complete pre-mixing gas/air supply system with a combustion gas single-barrel nozzle, so that the associate gas-burner system is noise-free and combustion-stable operation can occur, the above-mentioned U.S. patent application Ser. No. 10/978,571 provides an oscillation-damping air supply chamber connected upstream to the intake device of the combustion gas/air supply system, which is arranged outside of the combustion chamber on the heating apparatus. The oscillation-damping air supply chamber is provided with at least one air inlet. Also the entrance to the single-barrel combustion gas nozzle is arranged within the oscillation-damping air supply chamber.
This oscillation-damping air supply chamber, which is based on the known acoustic resonator used for sound analysis, is also called a Helmholtz resonator, It is also known for use in blower-assisted gas burners and it is formed with regard to its volume and its configuration so that its resonance frequency is tuned to the oscillations or standing waves arising in the combustion chamber and at least strongly damps and preferably cancels them by interference.
Because of the Helmholtz resonator no resonance oscillations exist in the combustion chamber, so that the gas burner system can be noise-free and operate in a combustion-stable manner.
Additional advantages include:                definite steady air supply,        no effect of air motion on the gas firing, since the gas firing occurs within the combustion chamber, so that it is guaranteed that the combustion processes are not impaired,        since the combustion air supply is definite and steady the quality of the combustion is improved, and        dust or dirt found on the ground or floor cannot be drawn in, since the combustion air supply is conducted in above it.        
It has been shown that under certain circumstances, especially when there is insufficient space in or on the gas-fired heating apparatus for the air supply chamber and thus the chamber cross-section is insufficient, the known oscillation-damping air supply chamber described in the above-mentioned U.S. patent application Ser. No. 10/978,571 and earlier unpublished German Patent application does not supply the gas burner with sufficient air. This effect causes poor combustion, i.e. high NOx/CO values, so that the allowed exhaust gas quality cannot be exceeded.